The issue of socioeconomic status (and social mobility) in relation to IQ is an empirical issue, and it is investigated empirically from time to time. An old article that I somehow missed at the time of publication, but which I coincidentally saw while searching for something else a few days ago, mentions some of the other influences on socioeconomic status besides IQ (that is, "controlling for IQ") in one study sample.
http://www.newscientist.com/article/dn11711-smarter-people-are-no-better-off.html What I find most innumerate about most popular literature on gifted education is the complete lack of discussion of error in IQ testing. On that issue, allow me to quote Lewis Terman, the developer of the Stanford-Binet IQ test.
"The reader should not lose sight of the fact that a test with even a high reliability yields scores which have an appreciable probable error. The probable error in terms of mental age is of course larger with older than with young children because of the increasing spread of mental age as we go from younger to older groups. For this reason it has been customary to express the P.E. [probable error] of a Binet score in terms of I.Q., since the spread of Binet I.Q.'s is fairly constant from age to age. However, when our correlation arrays [between Form L and Form M] were plotted for separate age groups they were all discovered to be distinctly fan-shaped. Figure 3 is typical of the arrays at every age level.
"From Figure 3 it becomes clear that the probable error of an I.Q. score is not a constant amount, but a variable which increases as I.Q. increases. It has frequently been noted in the literature that gifted subjects show greater I.Q. fluctuation than do clinical cases with low I.Q.'s . . . . we now see that this trend is inherent in the I.Q. technique itself, and might have been predicted on logical grounds." (Terman & Merrill, 1937, p. 44)
It's still true today that the error of IQ scoring is greatest in the range high above the median IQ. So particular test-takers will flip rank order with each other if each takes more than one IQ test. And that's why to talk about the "highly gifted" as a lifelong category one belongs to is just flat wrong from the get-go. But, yes, there is a whole lot of innumeracy in gifted education advocacy, which grates on my nerves, as I read John Paulos's book on that subject back when it was first published.
